Ως δείξη (αγγλ. deixis) ορίζεται η γλωσσική λειτουργία κατά την οποία χρησιμοποιούμε στοιχεία από το περιβάλλον τού ομιλητή (γλωσσικό και εξωγλωσσικό) προκειμένου να αναφερθούμε σε (να δείξουμε προς) αυτόν. Σε κάθε γλώσσα τα στοιχεία αυτά μπορούν να ερμηνευθούν μόνο αναφορικά με τον ομιλητή και αποκτούν νόημα μόνον εξαιτίας τής σύνδεσης με αυτόν. Οι γλωσσικοί τύποι που επιτελούν αυτή τη λειτουργία ονομάζονται δεικτικοί (deictic).

http://el.wikipedia.org/wiki/Δείξη

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Note added at 51 mins (2009-08-10 23:27:31 GMT)
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In linguistics, deixis refers to the phenomenon wherein understanding the meaning of certain words and phrases in an utterance requires contextual information. Words which have a fixed semantic meaning, but have a denotational meaning that constantly changes depending on time and/or place, is deictic. A word or phrase whose meaning requires this contextual information — for example, English pronouns — is said to be deictic. Deixis is closely related to both indexicality and anaphora, as will be further explained below. Note that this article deals largely with deixis in spoken language, but the same concepts can apply to written language and gestures as well. Also note that though this article is primarily concerned with deixis in English, it is believed to be a feature (to some degree) of all natural languages.[1] The term’s origin is Ancient Greek: δειξις, display, demonstration, or reference, the meaning "point of reference" in contemporary linguistics having been taken over from Chrysippus

http://en.wikipedia.org/wiki/Deixis

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Note added at 9 hrs (2009-08-11 07:41:00 GMT)
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It is not a point of reference, but the way of indicating a point of reference. It's the act of marking the orientation or position of entities and situations with respect to certain points of reference, e.g. "here/there" for place, "now/then" for time, "you/me" for person. The term "deictic center" refers to the point of place and time of the speaker.

You can find more information in George Yule's "The study of language" from CAMBRIDGE UNIVERSITY PRESS editions, and Edward Finegan's "Language - Its structure and use" from THOMSON WADSWORTH edition